John Rentoul: Labour's special delivery to Griffin

It was a terrific pantomime. Rarely is a live audience provided with such an obvious villain to jeer. When Nick Griffin went back to the end of the Ice Age as the source of his ideology, it was genuinely funny. When he the course of a single sentence went in from telling Jack Straw that "skin colour is irrelevant" to demanding that Britain be restored to its aboriginal "white" people, the audience, alert to absurdity, hooted with that rarity of polite society, derision.

The set design and props were wittily done, too, so that everyone on the panel wore a poppy, even though Armistice Day is several miles away, and Sayeeda Warsi, the Conservative peer, wore a huge floppy one so that she, at least, could not be outdone by the BNP in borrowing the sacrifices of previous generations.

A surprising feature of last week's programme, though, was the agreement that immigration was a serious problem that had not been handled well. Everyone – apart from the pantomime villain – agreed that immigrants make a valuable contribution to Britain, and hurried on to the "but". Everyone said we must listen to the concerns of the people who have voted BNP or might be tempted to do so, who are not racist (it doesn't do for democratic politicians to insult voters), but who had turned to Griffin's lot as a protest. Jack Straw was forced to say that Frank Field, who has demanded a population limit, is a very good friend of his. Griffin's only point scored, unless you count a man-not-the-ball tackle on Straw's conscientious objector father, was to mock Chris Huhne's positioning of the Liberal Democrats as an anti-immigration party too.

After all that fuss and bother, though, in which Griffin was rather messily exposed, to the satisfaction of the right-thinking classes at least, as what they knew him to be all along, what does it mean? The short-term result is bound to be to help the BNP win more votes at next year's general election than ever before. That may not seem to mean much. The party's progression through the New Labour years has been from 0.1 per cent in 1997, to 0.2 per cent in 2001, and 0.7 per cent in 2005. Last week's ComRes poll for this newspaper put the BNP on 1 per cent. In next year's election it may make it to one point something. It may even achieve the dizzying height of the 2.2 per cent won by the UK Independence Party in the last election, or the 2.6 per cent recorded by James Goldsmith's now-forgotten Referendum Party, two months before he, and it, expired in 1997. And how much difference would that make, really? The best estimate of the effect of the biggest recent fringe party irruption – the Referendum Party's – is that it cost the Conservatives four seats in Tony Blair's new dawn. If that's the worst of it, let's all calm down after the show and get on with the real politics of which biscuit the Prime Minister prefers.

But it could be worse than that. For all the pap about how the BNP's success reflects the failure of the "mainstream parties", it doesn't. It reflects a failure of one party in particular: the Labour Party.

The proof lies in maps prepared by Ben Page of Ipsos MORI, which compare the BNP vote in the London Assembly election of last year with that of the Labour Party at its lowest point in the 1970s. They are strikingly similar: sociologically and electorally, the BNP vote is the old Labour core vote. That was the secret of Boris Johnson's victory: he won that vote; Ken Livingstone, pursuing the rainbow coalition strategy of his early left origins, thought he could win by mobilising the ethnic minority vote. So it is not just the BNP vote next year that matters, although it will come at Labour's expense, but the hidden part of the iceberg that goes over to the Conservatives.

Jack Straw was the right Labour politician to be on Question Time last week, in two respects. One, he was responsible for the electoral systems that gave the BNP its representation: on the London Assembly and in Europe. But as Home Secretary he was also nominally responsible for immigration policy when it started to go wrong in Labour's first term. The pre-1997 Conservative government had restricted legitimate immigration tightly, so that, when five years of strong economic growth exerted a pull on international labour markets, economic migrants arrived in the form of asylum seekers. While Straw was at the Home Office, it was a clapped-out government machine trying hopelessly to keep up with international economic forces that threatened to overwhelm it. Tony Blair had to intervene and devote resources and prime ministerial attention to the issue in order to get the asylum system back towards a semblance of order. And then, in 2004, a new wave of unexpected immigration from Poland opened up when the European Union expanded from 15 to 25 countries.

That was the issue on which Huhne, the Lib Dem home affairs spokesman, retrospectively opposed immigration, on the grounds that the Government forecast had been too low. It was the point at which Labour's record on employment was exposed – all net new jobs since 1997 went to foreigners – which is why "British jobs for British workers" was such a poisonous sound bite for Gordon Brown. That was how Labour failed its old core vote.

The BNP is Labour's creature; its supporters are working-class voters who feel that they have been let down by a Labour government. BNP success is a measure of Labour's failure; of the collapse of the New Labour coalition of the white working class and the liberal middle class. More than that, it shows that our expectations about politics and social change have been reversed. Our default assumption is that government action is quick; social change slow. But immigration has changed parts of Britain more quickly than New Labour politics could anticipate or respond to.

What a paradox that New Labour, a political project designed to accommodate social change (all that stuff about globalisation, shaping it not resisting it), should have been caught out by the speed of change.

John Rentoul blogs at independent.co.uk/eagleeye